Forged flattop receiver and machined, free-float handguard are fused into a single component to provide a rock solid, quad-rail platform for maximum flexibility in mounting optics, backup sights, lights, vertical grips, and other accessories. The Versatile Interface Structure (VIS) offers a perfectly aligned top rail that cures the indexing problems common with flattop receivers and separate railed forends. Features four, MIL-STD 1913 Picatinny rails with side and bottom rails on the handguard. The continuous top rail from the back of the receiver to the front of the handguard eliminates the need for an extended base to mount a long eye-relief optic. Easy-to-remove bottom rail section assists in cleaning and maintenance, and allows attachment of an M203 grenade launcher, flare gun, tear gas launcher, or other SOPMOD component. Compatible with mil-spec lower receivers, bolt/carrier assemblies, and charging handles. Accepts any standard AR-15 barrel with a low profile gas block. Required barrel nut and wrench are included. Available with extended mid-length (VIS-2a), or rifle-length (VIS-3) handguard.